Biomolecules

• Living systems grow, sustain, and reproduce themselves
• Living systems are composed of non-living atoms and molecules
• The pursuit of knowledge of chemical processes within living systems falls under biochemistry
• Living systems are made up of complex biomolecules like carbohydrates, proteins, nucleic acids, and lipids
• Proteins and carbohydrates are essential constituents of our food
• Biomolecules interact with each other and constitute the molecular logic of life processes
• Simple molecules like vitamins and mineral salts also play an important role in the functions of organisms
• Structures and functions of biomolecules like carbohydrates, proteins, nucleic acids, and vitamins are discussed in this unit
• Carbohydrates are primarily produced by plants and form a large group of naturally occurring organic compounds
• Common examples of carbohydrates include cane sugar, glucose, and starch
• Carbohydrates have a general formula, Cx(H2O)y, and are considered hydrates of carbon
• Carbohydrates are classified into monosaccharides, oligosaccharides, and polysaccharides based on their behavior on hydrolysis
• Monosaccharides are carbohydrates that cannot be further hydrolyzed to give simpler units
• Oligosaccharides yield two to ten monosaccharide units on hydrolysis and are further classified as disaccharides, trisaccharides, etc.
• Polysaccharides yield a large number of monosaccharide units on hydrolysis
• Carbohydrates may be classified as reducing or non-reducing sugars
• All monosaccharides, whether aldose or ketose, are reducing sugars
• Monosaccharides are classified based on the number of carbon atoms and the functional group present in them
• Glucose is a common monosaccharide that occurs freely in nature and in combined forms
• Glucose is an aldohexose and is also known as dextrose
• Glucose is the monomer of larger carbohydrates like starch and cellulose
• The structure of glucose is determined by various chemical reactions and properties
• Glucose can be prepared from sucrose or starch through specific chemical processes
• Glucose has a D-configuration due to the comparison of the lowest asymmetric carbon atom with (+) glyceraldehyde
• The structure of glucose and glyceraldehyde is written with the most oxidized carbon at the top
• Glucose does not give Schiff’s test or form the hydrogensulphite addition product with NaHSO3 despite having the aldehyde group
• The pentaacetate of glucose does not react with hydroxylamine, indicating the absence of a free —CHO group
• Glucose exists in two different crystalline forms named a and b
• Glucose forms a six-membered ring in which —OH at C-5 is involved in ring formation
• The two cyclic hemiacetal forms of glucose differ in the configuration of the hydroxyl group at C1, called the anomeric carbon
• Fructose is a ketohexose found in fruits, honey, and vegetables
• Fructose contains a ketonic functional group at carbon number 2 and six carbons in a straight chain
• Fructose exists in two cyclic forms obtained by the addition of —OH at C5 to the —CHO group
• Disaccharides yield two molecules of monosaccharides upon hydrolysis with dilute acids or enzymes
• Sucrose is a common disaccharide that gives an equimolar mixture of D-(+)-glucose and D-(-) fructose upon hydrolysis
• Maltose is composed of two a-D-glucose units and is a reducing sugar
• Lactose is composed of b-D-galactose and b-D-glucose and is a reducing sugar
• Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages
• Starch is the main storage polysaccharide of plants, consisting of amylose and amylopectin
• Cellulose is a straight chain polysaccharide composed only of b-D-glucose units